If you're worried could you put them out during the daytime and bring them in at night or if it gets really wet or snows? Last year I put out our first batch at 2 to 3 days old but then the weather got seriously wet, cold and windy and we all buckled to and cleaned out a section of the shed in a morning (normally takes two days by hand), rebedded and kept the next batch in for a fortnight. hard work fetching and carrying but we didn't lose a lamb, and no coccidiosis either.